The present invention pertains to a packaging material with high printability and recyclability. The invention further relates to a method for producing such a packaging material.
The herein utilized expressions xe2x80x9crecyclabilityxe2x80x9d and xe2x80x9crecyclable raw materialsxe2x80x9d pertains to both material and energy recovery, such as the re-use of raw materials included in the packaging material when producing new packaging material, biological recovery of nutritious substances included in the packaging material by means of composing, energy recovery when combusting the packaging material, and the like.
Before or in connection with the use of the packaging material according to the invention in a package, a distance layer, included in the packaging material and comprising a matrix material and reinforcement fibres of cellulose, is expanded, wherein both the matrix material and the reinforcement fibres of cellulose are based on renewable and recyclable raw materials. Before the expansion, the distance layer has been applied onto and bonded to one or several surface layers which comprise cellulose fibres.
The surface layer(s) of the packaging material according to the invention provide(s) one or several smooth external surfaces with high printability. Furthermore, the packaging material according to the invention can, in a simple way, be re-used as a raw material for new packaging material. The packaging material according to the invention is intended to replace corrugated board and other packaging materials with similar fields of application. The packaging material according to the invention can, for example, be utilized in boxes or in protective, sheet-shaped wrappings, and also in applications with higher demands on printability than what is normal for conventional corrugated board.
Corrugated board is a long ago well-known packaging material and provides a number of significant advantages, such as low weight, high stiffness, recyclability and a proportionately low price.
The manufacture of corrugated board starts from liner and fluting. Thereby, liner refers to a paper grade with high tensile and tear resistance, which is intended to constitute surface layers in the finished corrugated board. Liner is preferably manufactured from unbleached sulphate pulp of softwood, but recently there has been a changeover to the utilization of recycled fibres, originating from corrugated board, as a raw material in so-called testliner.
Furthermore, with a view to improve the printability, the manufacture of multi-layered liner has been initiated, wherein the layer of the liner which is intended to be visible in a finished corrugated container is constituted of bleached chemical pulp and/or contains a filler with high brightness. As a rule, such liner is called xe2x80x9cwhite top linerxe2x80x9d.
The fluting is the undulating paper layer in corrugated board and has the task of providing the finished corrugated board with high stiffness and bulk, preferably by means of creating distance between the liner layers being part of the corrugated board. Fluting is generally manufactured from semi-chemical pulp, for example neutral sulphite pulp (NSSC).
There are corrugated board grades which have one single liner layer, which by means of a suitable adhesive has been attached to an undulating fluting layer in a corrugated board machine intended for this purpose.
However, it is occurring more frequently that two liner layers have been attached onto each side of an undulating fluting layer, or that the corrugated board consists of larger number of alternating liner and fluting layers, for example in the sequence liner/fluting/liner/fluting/liner. Thereby, the number of layers is determined, amongst other things, by the durability which is required from the finished corrugated container.
When manufacturing corrugated board, a frequently occurring chemical additive is different forms of starch or starch derivatives. Such an addition of starch can, for instance, be utilized as a dry strength agent in the liner production, or as an adhesive when converting liner and fluting into corrugated board.
The gradually increasing demand on resource economy and recycling have resulted in that corrugated board waste, and waste paper containing corrugated board, today can be recycled without any problems worth mentioning, as long as the main components included are cellulose fibres and starch and the starch content does not become too high. Certain synthetic adhesives, plastic layers, plastic particles and other additives in packaging materials, however, can render the recycling difficult and lead to disturbances in the production. Therefore, it is desirable that the recycled raw material which is re-used, for example in liner production, does not contain large amounts of such unwanted components, and that the content of starch or starch derivatives in relation to the content of cellulose fibre is not too high.
In connection with this, it may be mentioned that also other xe2x80x9cnaturalxe2x80x9d polymers, having similar properties as starch, can function well for recycling in a production process for liner, fluting or other raw material for packaging material. There are a number of such xe2x80x9cnaturalxe2x80x9d polymers, which are based on renewable raw materials and which, in principle, can be recovered in a corresponding way as starch, as long as the content of xe2x80x9cnaturalxe2x80x9d polymer in the process does not become too high. Examples of such xe2x80x9cnaturalxe2x80x9d polymers, which in this context usually can be placed on an equal footing with starch, are carboxy-methyl cellulose (CMC), alginate, casein, animal glue, polylactides (PLA), pentosanes, chitin and other polymers which have been manufactured from natural, in the short term renewable, non-fossil raw materials.
It has preciously been suggested to produce packaging material out of expanded starch. Accordingly, the patent publication U.S. Pat. No. 5,035,930 discloses a biodegradable shaped product comprising an expanded starch, having a high amylose content of at least 45%. The expanded product is claimed to have a low density, a closed cell structure, and to be compressible. In U.S. Pat. No. 5,035,930, the use of the expanded starch material in a biodegradable packaging material, such as an insert or a loose fill, is also disclosed.
Furthermore, the patent publication EP 0 696 612 A2 discloses biodegradable foamed articles and a process for their preparation. The foamed articles are claimed to have a density between 5 and 300 kg/m3 and are obtained by means of agglomerating foamed particles having a composition comprising a themoplastic starchy material or a thermoplastic natural polymer capable of absorbing water when converted into the thermoplastic state, a thermoplastic polymer and water. The task of the thermoplastic polymer is claimed to be to improve the strength of melted composition, and to obtain foamed particles with high elasticity and low moisture sensitivity. In EP 0 696 612 A2, if is also disclosed that sandwich structures easily can be formed by means of bonding one or several sheets or panels which have been obtained by means of agglomeration of foamed particles, and that the biodegradable sheets or panels can be joined together with paper sheets, cardboard sheets or a film or a sheet of a biodegradable plastic material or of a conventional plastic material. Furthermore, its is disclosed that cellulose fibres can be included in such sheets or panels together with the foamed particles, WO 94/05492 discloses a laminate comprising hardened starch which is bound to another material. The laminate is obtained by extruding a suspension of expanded starch between two outer layers.
Something which might be perceived as a disadvantage with conventional corrugated board is that the undulating fluting layer is attached to the liner only at its wave crests. This often results in problems with so-called xe2x80x9cwashboarding effectsxe2x80x9d. This Implies that the external surface of the corrugated board, i.e. the liner, assumes a washboard-like structure with wave crests and wave troughs. This results in a heavily impaired printablity and, amongst other things, implies that printing of corrugated board hitherto in general has been limited to comparatively simple flexographic printing techniques. Previously known packaging materials of expanded starch, without any surface layers of paper, can only be printed with the use of special printing techniques. Furthermore, the recovery of such packaging materials into raw material for new packaging material can exhibit certain difficulties, and restrict the disposal possibilities to composting or waste incineration.
Problems with uneven outer surfaces and unsatisfactory printability can arise also when packaging materials comprising foamed starch particles are concerned, which particles have been formed into panels or sheets in a preexpanded condition and which thereafter, by means of laminating, have been provided with surface layers of paper. The reason for this is that the expanded starch particles, having a density/hardness being different from the binder which keeps such a panel or sheet together, easily can create irregularities in an external surface layer of paper and result in an impaired printability. Furthermore, the recycling of such materials can offer some difficulties because of the proportionately large number of included chemical components, which also may comprise chemical compounds which are based on undesired, non-renewable, fossil raw materials.
Accordingly, a first object of the present invention is to provide a method for the manufacture of a packaging material which eliminate the abovementioned problems with the prior art, and which provides at least one external surface with high printability and which, furthermore, provides high recyclability into raw material for renewed production of packaging material.
Another object of the invention is to provide a packaging material which is produced in accordance with the method. A further object of the invention is to offer a packaging material which reduces transport and storage costs and which increases the options when converting the material into packaging blanks, or packages.
In accordance with the following claim 1, this objects of the invention are achieved by means of a method for the manufacture of a packaging material for the production of packaging blanks and packages and comprising providing at least one surface layer in the form of a continuous material web and substantially comprising of cellulosic fibres and applying a distance layer thereto, said distance layer comprising a matrix material and cellulosic reinforcement fibres, so that said surface layer is bond to said distance layer. The method is characterised in that the matrix material in the distance layer exists in an expandable form during application thereof to the surface layer and in that the matrix material is expanded in a separate process step, subsequent to the application step.
A packaging material in accordance with the invention and comprising at least one surface layer substantially consisting of cellulosic fibres and at least one distance layer, wnerein said distance laye comprises a matrix material and reinforcement fibres, preferably cellulosic reinforcement fibres, and wherein said distance layer is bonded to said surface layer is primarily charaterised in that the matrix material in the distance layer is in an expandable state.
It is advantageous if both the matrix material and the reinforcement fibres are based on renewable and recyclable starting materials. In accordance with the invention, the matrix material in the distance layer is in an expandable state and the distance layer is an even, continuous layer which is bonded to the surface layer with the multiplicity of bonding spots which are substantially continuously distributed in the plane of the packaging material, between the distance layer and the surface layer so that an even outer surface exhibiting high printability is created on the surface layer. Furthermore, in accordance with the invention, the amount of matrix material, cellulosic fibres in the packaging material and the strength of the bonding spots when the material is in a completely wet state are adapted in order to allow for reclaiming raw material for renewed production of the packaging material.
In order to achieve the objects of the present invention, the type of matrix material based on renewable and recyclable raw material, which is used in the distance layer, is in principle irrelevant as long as the obtained packaging material is able to fulfil the features which are defined in the following claims. Accordingly, the utilized matrix material has to be expandable, applicable as an even, continuous layer, and enable recycling of the packaging material. Consequently, the utilized matrix material has to contain some form of expansion agent, for example water, a chemical compound which emits gas when heated, or the like.
The application of the distance layer can take place with any suitable type of equipment having the ability to form and apply a distance layer comprising matrix material and reinforcement fibres of cellulose, as long as the applied distance layer fulfils the requirements which are made according to the invention.
A distance layer for use in the packaging material according to the invention, for example, can be formed and applied analogous to previously known extrusion technique for starch, wherein the starch is brought into a thermoplastic state in an extruder and is formed into a web-shaped distance layer which is applied onto a surface layer or between two surface layers, for example of liner. Thereby, the distance layer can be expanded in connection with the extrusion by means of water, included in the starch structure, which because of the high temperature during the extrusion forms expanding water vapour, or the expansion can take place by means of another suitable expansion agent and/or in a process stage subsequent to the forming/application.
Accordingly, the expansion of the distance layer can take place with any preciously known technique, and can for example comprise heat supply, another suitable energy supply, or another previously known activating agent for expansion.
A major advantage offered by the invention is that it is possible to product packaging material in the form of continuous webs and subsequently, independently of the production of the packaging material, convert the packaging material into packaging blanks and finished packages. Due to the fact that the packaging material in accordance with the invention is expandable after lamination of the distance layer or distance layers to the surface layer or surface layers, the packaging material can be transported and stored in roll form. Conversion into packaging blanks and finished packages can subsequently be made by a packaging manufacturer who is then able to freely decide the degree of expansion of the material and the shape and size of the individual packaging blanks/packages. Accordingly, the invention offers unique possibilities of flexibility in the conversion steps.
The cellulose fibres in the surface layer(s) can be of any suitable type, but are preferably of the type which is used in conventional production of corrugated board. The surface layer(s) can also be white top liner, testliner or another suitable paper grade, such as cardboard.
Furthermore, the reinforcement fibres of cellulose can be of any type, based on renewable and recyclable raw material, but are advantageously the same type of fibres as the cellulose fibres in the surface layer(s). When forming the distance layer, suitable means for adding the reinforcement fibres of cellulose to the matrix material has to be provided before the forming.